Abstract

Two series of layered perovskite oxides continue to attract research attention. One series is the Ruddlesden-Popper (R-P) oxides,1 $A_2[A_{n-1}B_nO_{3n+1}]$, whose members such as 2-4 $K_2La_2Ti_3O_{10}$, $K_2SrTa_2O_7$, and $NaLnTiO_4$ (Ln = La or rare earth) have been investigated for a wide variety of properties, which include ion-exchange,2,3 intercalation,5 exfoliation,5 topochemical dehydration,6,7 reductive transformation to higher members,8,9 and photocatalytic activity for decomposition of water.10 The other series is the Aurivillius (A) phases,11 $(Bi_2O_2)[A_{n-1}B_nO_{3n+1}]$, which are well-known high-temperature ferroelectric materials. In recent times, members of this series, for example, $Bi_2SrTa_2O_9$ and Lasubstituted $Bi_4Ti_3O_{12}$ in thin-film geometry, have been shown to possess nonvolatile ferroelectric memory characteristics that are promising for computer memory applications.12,13 Considering that the 2D-perovskite unit, viz., $[A_{n-1}B_nO_{3n+1}]$, is common for both of the series of oxides, one could envisage the following from a crystal-chemistry standpoint: Transformation of R-P to A series and vice versa by exchanging the interlayer entities between the perovskite sheets, and bridging of the two series by sequentially arranging the interlayer entities between the perovskite sheets. The R-P f A and A f R-P transformations have recently been achieved 14,15 by innovative chemical reactions involving metathesis/selective acid leaching. Bridging of the two series of layered perovskites wherein structural units of R-P and A phases are stacked one over the other to give the layer sequence, $[Bi_2O_2]-
[A_{n-1}B_nO_{3n+1}]A_2[A_{n-1}B_nO_{3n+1}]$, has, however, not been reported so far. We report in this Communication the synthesis and structure of new layered perovskite oxides of the formula, $(BiO)-LnTiO_4$ (Ln = La, Nd, Sm), which could be regarded as n = 1 members of this series, $A(BiO)[A_{n-1}B_nO_{3n+1}]$, bridging the R-P and A layered perovskites for the first time.